The present disclosure relates to data encoders, decoders, equalizers and detectors for use with communication channels, and more particularly, to systems and methods for data detection over inter-symbol interference channels with correlated noise.
Storage/retrieval systems and data transmission systems often utilize detection/decoding schemes for data detection due to the presence of inter-symbol interference (ISI). Noise encountered in magnetic recording channels typically has two components, electronic noise and media noise. The electronic noise does not depend on data patterns. However, the media noise (jitter) that arises from deviations in the position and width of transition pulses is pattern dependent. Media noise is more severe when there are more transitions in the signal pattern. Consequently, noise in magnetic recording channels is pattern dependent. Moreover, the noise seen by a channel detector is correlated due to “partial response equalization”, which is employed to decrease the complexity of the channel detector.
To detect information from ISI channels, channel detectors often utilize a trellis-based maximum a-posteriori (MAP) algorithm, a Viterbi algorithm, or a soft output Viterbi algorithm (SOVA). For coded systems, a soft output detector, such as a MAP-based detector, a SOVA detector, and the like, are typically used. The soft output detector applies an algorithm that assumes that the noise on the ISI channel is white Gaussian while computing the soft channel outputs.
Belief propagation (BP) based soft-input soft-output (SISO) detectors have been proposed to detect ISI channels with additive white Gaussian noise as an alternative to MAP and Viterbi-based channel detectors. Generally, belief propagation has been employed in artificial intelligence systems and is known as a message passing (sum/product) algorithm. Typically, belief propagation works on a factor graph while calculating a posterior probabilities of channel inputs, and it assumes the presence of additive white Gaussian noise. However, not all ISI channels have additive white Gaussian noise. For example, magnetic recording channels that are equalized to a partial response (PR) target have correlated noise due to the linear equalizer used to shape the channel impulse response (partial-response equalization).
There is an ongoing need for data detection systems and methods that can detect data on both coded and uncoded channels, such as magnetic recording systems. Some of the embodiments of the present invention address these and other problems in the prior art, and provide advantages of conventional systems.